This invention relates to apparatus for use in analytical instruments and in particular it relates to apparatus for use in instruments such as autosamplers for supporting and retaining substances in the correct disposition with regard to cartridges on such a machine. Autosamplers, such as the Hewlett Packard HP 7673A, generally comprise a carousel having a plurality of apertures into which sample vials can be inserted so that a sampling needle can be lowered into the vial to obtain a sample of a substance held by the vial.